Conventionally, halogen lamps have often been used as headlamps for cars or the like (vehicle headlamp). However, in recent years, headlamps that use HID lamps (High Discharge Lamp) are increasing in its number.
Headlamps are generally configured capable of forming a low beam light distribution pattern (illuminated region), which pattern has a cut-off line on its upper edge. This is to ensure forward visibility for the driver while preventing a driver of an oncoming vehicle from becoming dazzled by the headlamps.
Headlamps which use light emitting diodes (LED) as their light sources have been developed eagerly recently, which LED is low in its electricity consumption. For example, Patent Literature 1 discloses a headlamp that forms an illuminated region 111 by combining patterns 111a to 111c that are obtained by projecting light on different regions with respective light source units (hereinafter, called region partitioning headlamps), as illustrated in FIG. 37.
Moreover, Patent Literature 2 discloses a headlamp that forms an illuminated region 211 by overlapping patterns 211a to 211d of respective light source units in a superposed manner (hereinafter, called superposed headlamp), as illustrated in FIG. 38.